In recent years, various LED light source products have been developed with improved brightness and other characteristics. In particular, white LED light sources that can be realized by development of blue LED devices have advantages common to LED light sources, such as low power consumption and long life, and therefore receive attention as new illumination light sources that can replace fluorescent and incandescent lamps that are used for general illumination and interior lighting at present.
FIG. 18 is a cross-sectional view of an LED light source 10.
In LED light source 10, an LED device 101 is disposed on a substrate. In the substrate, a pattern of a wiring conductor 103 for supplying electric power to the LED is formed on a base material 102. Further, LED device 101 is mounted on the substrate by using die bonding paste, Ag paste and the like. Further, LED device 101 is supplied with electric power from the outside via wiring conductor 103 on the substrate and bonding wires 104 and emits light.
Around LED device 101, a sealing material 106 is formed for protecting LED device 101. Further, a first fluorescent material is mixed in resin of sealing material 106. The fluorescent material absorbs and wavelength-converts a portion of the light emitted from LED device 101 to emit light from itself. Further, a reflective frame 105 is disposed outside sealing material 106.
In LED light source 10, a nitride compound semiconductor emitting blue light is used as LED device 101, while an yttrium-aluminum-garnet (YAG) fluorescent material activated with cerium is used as the first fluorescent material. As a result, white LED light source 10 emits pseudo white light in which the blue light from LED device 101 and the yellow light from the first fluorescent material are mixed together.
LED light source 10 in which LED device 101 and the first fluorescent material are combined to emit the pseudo white light has a disadvantage in that chromaticity varies between individual LED light sources unless a ratio between the blue light and the yellow light is constant.
It is thought that chromaticity variation between individual LED light sources 10 occurs due to unevenness in the amount of the sealing material, dispersion condition and particle size of the fluorescent material, and the like.
FIG. 19 is a diagram illustrating an example of chromaticity coordinates.
For example, as the amount of fluorescent material in sealing material 106 increases, the chromaticity of LED light source 10 is shifted from the white region toward the yellow side on the chromaticity coordinates and as the amount of fluorescent material in sealing material 106 decreases, the chromaticity of LED light source 10 is shifted from the white region toward the blue side on the chromaticity coordinates. It is difficult to avoid such variation of the chromaticity between the individual LED light sources in the manufacturing process, and therefore it is very difficult to mass-produce LED light sources having a constant chromaticity only.
Patent Document 1 describes a method for adjusting chromaticity by changing a thickness of an upper part of a transparent resin layer after hardening by polishing, coating and the like so as to change light paths from an LED device.
FIG. 20 is diagram describing the chromaticity adjustment method as set forth in Patent Document 1.
In LED light source 20, an LED device 101 is disposed on a substrate comprised of base material 102 and wiring conductor 103 and it is electrically connected with wiring conductor 103 via bonding wires 104. A sealing material is filled inside reflective frame 105 disposed on the substrate. At the lower part of the sealing material, a first fluorescent material 21 is deposited and, at the upper part of the sealing material, only a transparent resin 22 is hardened.
FIG. 20(a) illustrates an example in which transparent resin 22 at the upper part is polished till a target chromaticity is obtained. In the example of FIG. 20(a), transparent resin 22 is polished until the resin surface is lowered from position 23 before polishing to position 24 after polishing. As a result, the light is confined in a narrower space (of the transparent resin) and its reflection is repeated more frequently, so that the probability that the light from LED device 101 encounters the first fluorescent material increases, and thus the wavelength-conversion rate also increases. Therefore, the chromaticity of LED light source 20 is adjusted from blue to yellow.
FIG. 20(b) illustrates an example in which further resin is added above position 23 of the resin surface so as to raise the resin surface to position 25. In the example of FIG. 20(b), as the amount of resin increases, the light passes through a larger space (of the transparent resin), so that the probability of light from LED device 101 encountering the first fluorescent material decreases, and thus the wavelength-conversion rate also decreases. Therefore, the chromaticity of LED light source 30 is adjusted from yellow to blue.
Thus, it is possible to adjust the chromaticity by simply increasing or decreasing the amount of the transparent resin. However, if there is any restriction on an outer shape of the LED light source, it is difficult to increase or decrease the amount of the transparent resin. Further, when the transparent resin is polished, the LED light source may be impacted, scratched or otherwise damaged, so that malfunctions may occur such as, for example, breakage of the bonding wires, damage of the reflective frame and the like.
Patent Document 1: JP-A-2004-186488 (page 4, page 8 and FIG. 2)